The Aquaporins NtAQP1 and NtPIP2;1 from Nicotiana tabacum exhibit different water conductivities in functional characterization assays despite similar amino acid sequences in the selectivity filters. NtPIP2;1 expression in Xenopus laevis oocytes caused high water permeability whereas NtAQP1 reveals low water conductivity. The aim of this thesis was to identify the structural basis and/or regulation mechanisms which affect the functional difference of NtAQP1 and NtPIP2;1. The exchange of the amino acid sequence of the n-terminus of NtAQP1 with the of NtPIP2;1 increased significantly the water conductivity of the chimeric protein compared to the native NtAQP1. Accordingly the N-terminus of NtPIP2;1 contributes to the mechanism causing the functional difference. In Addition direct interaction of NtAQP1 and NtPIP2;1 in a heterotetramer led to water channel function of NtAQP1. This was indicated by connecting the molar ratio of NtAQP1 and NtPIP2;1 in artificial heterotetramers to the water permeability of the membrane. Beside protein-protein interactions post translational modifications like phosphorylation or protonation could modify the function of plant aquaporins. Following analysis of modifications on the function of NtAQP1 and NtPIP2;1 phosphorylation could be excluded as a regulative mechanism. The protonation of NtPIP2;1 caused decreased water conductivity of the channel, however by a not yet identified mechanism.